If someone has a criticism it means they want to give you feedback on what you're doing for them – that means an opportunity to learn more about the person who you're working for and how to convert them into a satisfied customer or audience member.
Take a moment to think before you respond to what they're saying – in business, working with someone who is patient and able to receive and act on criticism means both parties can work towards a better outcome.
For a play or production, it might mean getting to know what your audience actually want.